Wood screw and method for making same

Abstract

A wood screw has a resilient shaft carrying a spiral thread of nominal pitch from the tip. The thread is interrupted at a plurality of intervals and the shaft is torsionally resilient. When the screw fastener is driven, the shaft twists and contracts so that the thread in the mating material has a pitch which is less than the nominal pitch. The interrupted thread may consist of a plurality of resilient lobes.

I claim: 
     
       1. A screw fastener for insertion into an object comprising: a screw head, a shaft formed integrally on said screw head, and drag means for shortening the length of the shaft as the fastener is inserted into the object; wherein said drag means includes a thread of nominal pitch spiralling around said shaft from a starting tip, said thread being interrupted at a plurality of intervals; and wherein said shaft is torsionally resilient so that as said fastener is inserted into said object, said shaft twists and contracts to produce a thread having a pitch which is less than said nominal pitch; and wherein the thread includes a plurality of lobes having an elongate cross-section which lies in a plane of said thread and wherein the elongate cross section is substantially petal shaped.   
     
     
       2. A screw fastener for insertion into an object comprising: a screw head, a shaft formed integrally on said screw head, and drag means for shortening the length of the shaft as the fastener is inserted into the object; wherein said drag means includes a thread of nominal pitch spiralling around said shaft from a starting tip, said thread being interrupted at a plurality of intervals; and wherein said shaft is torsionally resilient so that as said fastener is inserted into said object, said shaft twists and contracts to produce a thread having a pitch which is less than said nominal pitch; and wherein the thread includes a plurality of lobes and wherein adjacent portions of the thread at the same angular position along the shaft are separated from each other by a distance equal to approximately twice the width of one of the plurality of lobes.